Magnetically actuated switch device



United States Patent 3,142,762 MAGNETICALLY ACTUATED SWITCH DEVICE George Frederick Kelk, Willowdale, Ontario, and Joseph Tanshman, Downsview, Ontario, Canada, assignors to George Kelk Limited Filed Jan. 22, 1960, Ser. No. 4,111

4 Claims. (Cl. 307-38) This invention relates to a magnetically actuated switch device.

Magnetically actuated switches are known in the sense that a pivotal or hinged movable switch armature may be caused to be moved into or out of position of physical contact for completion of an electrical circuit by the presence of a permanent magnet physicaly moved into and out of association therewith. Such prior art devices may be obtained in the form of single pole double throw relays as manufactured by C. P. Clare Company, Chicago, under catalogue No. RP. 5441. The permanent magnet used in this form of prior art may be formed of two General Electric sintered Alnico II magnets, catalogue No. 22Ul7B. It is known that such magnetically actuated relay devices have been arranged in decade array for successive magnetic actuation as a digitizing device. It is characteristic of such prior art magnetic switch devices that electrical contacts used in the switching action may be subject to failure by wear, fatigue or incorrect orientation limiting the usefulness or life thereof. Mechanical limitations also limit the speed of operation.

It is the main object of this invention to provide a magnetically actuated switch device devoid of mechanicalelectrical contact components and thus of substantially indefinitely long life and adapted for high speed actuation.

It is a further object of the invention to provide a switch device adaptable for digital converter use.

With the foregoing and other objects in view, the invention generally concerns an electrical switch device for an exterior electrical circuit and comprising resonant circuit components in the form of a condenser, a coil and a ferro-magnetic member proximate said coil, said components being electrically and magnetically proportioned and connected for resonance of said coil at a predetermined frequency in said circuit; an energizing source of said frequency for said circuit; means for moving said member into and out of proximity with said coil thereby selectively to provide resonant and non-resonant states in said circuit.

Other objects of the invention will be appreciated by the study of the following specification taken in conjunction with the following drawings:

FIGURE 1 is a perspective view of one of a preferred form of ferro-resonant digitizer according to the invention and utilizing switch device of the invention as set forth herein the input and output terminals of the digitizer being hidden from view;

FIGURE 2 is an elementary circuit diagram of a switching device according to the invention;

FIGURE 3 is an operating voltage range chart illustrating the effect of operating voltage on the elementary circuit of FIGURE 2; and

- FIGURE 4 is an electrical schematic illustrating the ar- "ice rotatable in the direction of the arrow Y and an electro magnetic or ferro-magnetic armature member 11 extending radially therefrom the said member preferably being in the form of a permanent magnet such as Alnico II. Shaft 10 is centrally mounted within tube 12 carrying the equally spaced toroid coil inductances 13 which as shown may be ten in number. Each of the coils 13 has associated therewith a condenser 14 preferably likewise spaced on the tube 12 in any suitable manner such as by terminal members (not shown) which may extend outward from the tube which latter is formed of insulating material. Motion of the armature member 11 due to rotation of shaft will cause a change in the inductance of the coil with which it is in closest proximity. When utilizing a permanent magnet member 11 a frequency can be selected for design of the coil condenser and the magnet at its nearest position such that a resonant peak exists at the proximate position of the magnet. Accordingly energization of the coil with a signal of the selected predetermined frequency causes a high current condition to occur.

As will be evident from examination of FIGURE 5, assuming the energizing signal generator 15 to be energizing the coils 13 in a parallel circuit by inner and outer ring connectors 16 and 17, current from source 15 will produce a flux level in all of the inductances or coils. However, the presence of an armature 11 in proximity to one of the coils 13a will cause the inductance thereof to be reduced very substantially corresponding to a condition of circuit resonance thereby reducing the effective voltage across the remaining circuits in parallel and preventing the other coil circuits from achieving a resonance condition as will be more apparent upon consideration of FIGURES 2 and 3.

Referring to FIGURES 2 and 3, two toroid windings 18 and 19 on high permeability cores 20 and 21 are connected with condensers 22 and 23 respectively in series with loads 24 and 25 in parallel across the frequency generator source 26 through impedance 27. By way of example the coils 18 and 19 may each be formed of 132 turns of #36 enamelled wire on a core of in. mean annular diameter .002 in. thick and .080 in. wide, the core material being a ribbon of high permeability material as for example .00025 in. thick high permeability magnetic tape of the kind used for forming high permeability audio frequency filter choke and transformer type cores. Source 26 may provide a 40 kc. frequency alternating current energizing signal of 30 volts open circuit potential. The impedance 27 may conveniently be in the form of a condenser of .005 microfarad. Condensers 22 and 23 should be of a capacity to resonate at the minimum inductance of coils 18 and 19 at 40 kc. and thus may be about .003 microfarad for the inductance of the core and coil structure described. Switching load 24 by way of example may be a lamp havinga filament rating of 1.5 volts and 60 milliamperes. The balance load lamp 25 maybe of a value corresponding to the so-called hot resistance of lamp 24, that is about 7.5 ohms. The lamp may be controllably switched from a de-energized to an energized state by moving permanent magnet 28 between the coils 18 and 19 depending upon the potential of the source 26.

Referring to FIGURES 2 and 3, the desired function and operation of the elementary circuit illustrated in FIG- URE 2 will be evident from a review of the following typical experiments.

Experiment l.0peration Class I The magnet 28 was removed from its position between the coils 18 and 19. Slider 29 inFIGURE 2 determined the voltage obtainable from the voltage dividing network 30 energized by the generator 26. The slider 29 was moved to develop a voltage E for which both lamps 24 and 25 were illuminated corresponding to a condition of resonance in the circuits 18, 22 and 19, 23. The condition of resonance was accompanied by a reduction in the inductance value of the coils 18 and 19 and the selfsaturation of the coils 18 and 19 due to the passage of high current through the coils in the resonant condition of their circuits. i

Experiment 3.Class III Operation The association of a permanent magnet with the cores 20 and 21 will effect saturation thereof to a degree depending upon the proximity of the magnet to each core. When magnet 28 was placed midway between the two cores, one could achieve operation of one lamp while the magnet was stationary but at a different and slightly lower applied voltage E It now the magnet was moved toward the core of the coil in circuit with the glowing lamp no change was observed. If however the magnet was moved toward the core of the coilof the circuit with the non-glowing lamp, the increase in inductance of coil 19 by reason of saturation of the core 21 thereof due to presence of the magnet in proximity therewith initiated a resonant condition increasing the current inthe impedance 27 to reduce voltage drop across the first resonant circuit 18, 22 to a value insufiicient to maintain resonance therein whereby lamp 24 was extinguished and lamp 2 glowed.

Experiment 4,- Class IV Operation The permanent magnet was placed proximate to one of'the cores so the core 20 and voltage'ERwas controlled by moving slider 29 from a position delivering a very small voltage'to'a'valu'e for which the lamp 24 suddenly glowed'corresponding to a condition of resonancein the circuit 18', 22. The triggering voltage for resonance was slightly less than for'the previous experiment. The magnet was then movedtoward the other core 21 until it arrived at a position proximate with same. The degree of core saturation caused 'by the permanent magnet being greater than the degree of core saturation through the core 18 during resonance then the larnp extinguished before the permanent magnet arrived sufficiently close to core 21 to initiate resonance in coil 19 and illumination of lamp It will be apparent that the switching function accomplished by motion of the permanent magnet in this experiment it is characterized by what may be referred to in the switching arts as contact separation,'i.e. a position of the magnet for which neither lamp will glow.

Using the circuits shown' above but with only two resonant circuits connected, it was found that 120 kc. was the best operating frequency. The generator voltage was brought up slowly from zero with no magnet located near the cores. It was found that'one lamp came on at a generator voltage of 9.5 volts (Class II) and that the second lamp came on at agener'ator voltage of 10.8 volts (Class I).

With the magnet located approximately mid way between the two cores, this was repeated and it was found that one lamp came on at 5.5 volts (Class III) and the second lamp came on at 7.5 volts (Class III-Class I).

With the magnet placed to have maximum influence on one of'the cores, the lamp associated with this core 'came'on at 'a voltage of 5 volts (Class IV).

The best operation was found to be at kc. with an applied voltage of 6.8 volts.

It was found that a difference of approximately 1 was obtained in the position of the magnet between the coils at the instant of switching, depending on the direction of motion, thus the pole pieces moved about 0.5 past the mid point between coils before the lamp being approached by the magnet came on, and when the direction of the magnet was reversed, it had to move about 05 back past the centre line before the lamp now in front of it came on.

This overlap could be varied by changing any of the operating conditions of the circuit such as generator voltage and frequency, or magnetic strength.

It is possible by means of lower generator voltage or lower magnetic strength, to have a gap or zone between the lamps where the magnet may be located without producing resonance in either of the adjacent circuits.

At a frequency of 120 kc. a gap of 2 was found with a generator voltage of 5.5 volts, and at 7.2 volts (the maximum voltage available) an overlap of 2 was obtained.

The values of L, C and frequency are chosen such that in order to become resonant a value of inductance must exist which occurs only with saturation of the core, either by means of a permanent magnet nearby, or by means of the alternating current itself. Resonance may also be established by means of a high initial voltage from the generator.

In FIGURE 4, when the generator is first energized none ofthe resonant circuits are resonant and therefore little current is drawn by them. Thus the voltage across the resonant circuit is high and one of the circuits becomes resonant. As soon as it does so its terminal impedance becomes quite low so that by reason of theseries impedance (.02 mfd. in the circuit) the voltage across its terminals 'and therefore across the terminals of the other circuits is too low to allow them to resonate.

Movement of the permanent magnet from coil to coil is able to bring successive circuits into resonance, thus causing a cessation of resonance in the previous circuit.

'In FIGURE 4, the schematic of the digitizer of FIG- UREl is shown in which components are identified according to that figure. In this figure the resistance 31 corresponds to the impedance 27. Switch 32 may be utilized for connecting and dis-connecting the source of energizing current. The terminals 34 and 33 through to 33 may be connected to'a high impedance indicator or coupling device for a utilizing circuit (not shown). It the indicator is of a series current type such as a lamp device'as described'in reference to FIGURE 2, the lamp should be of low resistance to form a negligible portion of the circuit when in resonance.

In operation according to Class III as described herein, the magnet 11 proceeds in FIGURE 4 to effect triggering or actuation of resonance in succeeding coil circuits, a resonance condition occurring in each successive circuit upon the extinguishing of resonance in the previous circuit. The circuit may thus be provided in ring like form for utilization as a digitizer and in which the contact separation or overlap may be controlled by a selection of the striking or triggering voltage E as described.

Thus the present invention in enabling the setting of the triggering voltage can effect the control of the switch gap or overlap as described herein to achieve the characteristics desired in the switching operation.

As an alternative to controlling the voltage E the various coil cores'may be biased magnetically in the manner indicated in FIGURE 1 by passing the conductor loop 35 through all cores and passing a direct current therethrough. By this means also, the saturation level in the cores may be brought to a value sufiiciently close to the desired value of saturation such that the influence of the permanentmagnet 11 need only be sufficient'to eifect triggering of resonance. Logically also, each of the cores may have a permanent magnet associated therewith to effectively bias same to a saturation level less than but near to the operating saturation level of said cores during resonance.

It will be apparent from the foregoing that the invention contemplates a magnetically actuated switch device adapted to provide an electrical signal responsive to a physical positioning of a switching member and zero signal responsive to another position of said member and comprising in combination, a source of alternating current, a coil having a saturable core and a capacitance in resonant circuit with said source, a magnetic switch member, means for positioning said magnet a pre-determined spacing from said core, means controlling the voltage of said source to a value sufllcient only to trigger resonance in said circuit at said pre-determined spacing, means for moving said magnetic member away from said core to a position of greater spacing therefrom sufiicient to extinguish resonance in said circuit and means for extracting a resonant electrical current signal from said circuit responsive to the positioning of said magnetic member at said pre-determined spacing from said core.

It will also be apparent that the invention contemplates the method of actuating a resonant circuit having a source of alternating current therefor, said circuit containing a coil having a saturable core and a capacitance, said method comprising controlling the voltage of said source to a value lower than that sufiicient to effect resonance in said circuit and controllably placing a magnetic member or flux into association with said core to effect saturation of same thus to reduce the effective triggering voltage of said circuit to a value equal to or less than the controlled voltage of said source, thus to initiate resonance and with drawing the permanent magnet from saturable association with said core.

What We claim as our invention is:

1. A magnetically actuated switch device adapted to provide an electrical signal responsive to a physical positioning of a switching member and zero signal responsive to another position of said member and comprising in combination: a source of alternating current; a coil having a saturable core and a capacitance in resonant circuit with said source; a magnetic switch member; means for positioning said magnetic member a pre-determined spacing from said core; means controlling the voltage of said source to a value suflicient only to trigger resonance in said circuit at said pre-determined spacing; means for extracting a resonant electrical current signal from said circuit responsive to the positioning of said magnetic member at said pre-determined spacing from said core; at least one other resonant circuit in parallel arrangement with said first mentioned resonant circuit and having a similar coil, saturable core and capacitance; and a common impedance interposed between all the said resonant circuits and said source.

2. A device as claimed in claim 1 in which at least ten resonant circuits are connected through said common impedance to said source.

3. A device as claimed in claim 1 and means for biasing the saturation of said saturable cores.

4. A magnetically actuated switch device adapted to provide an electrical signal responsive to a physical positioning of a switching member and zero signal responsive to another position of said member and comprising in combination: a source of alternating current; a series impedance for said source; a coil having a saturable core and a capacitance in resonant circuit connection therewith; means connecting said resonant circuit to said source through said impedance; a magnetic switch member; means for positioning said magnetic member a pre-determined spacing from said core; means controlling the voltage of said source to a value sufficient only to trigger resonance in said circuit at said pro-determined spacing; means for extracting a resonant electrical current signal from said circuit responsive to the positioning of said magnetic member at said pre-determined spacing from said core; at least one other resonant circuit in parallel connection to said source and impedance with said first mentioned resonant circuit and having a similar coil saturable core and capacitance; means supporting said cores for said coils in pro-determined successive spacing .between adjacent cores; and means conveying the said magnetic member successively into association with said cores at said pre-determined distance thereby to extinguish a resonant condition in said first mentioned circuit while causing the generation of a resonant condition in the successive core and circuit.

References Cited in the file of this patent UNITED STATES PATENTS 2,653,254 Spitzer et a1. Sept. 22, 1953 2,906,942 Mittag Sept. 29, 1959 2,922,994 Kennedy Jan. 26, 1960 2,930,034 Berman Mar. 22, 1960 

4. A MAGNETICALLY ACTUATED SWITCH DEVICE ADAPTED TO PROVIDE AN ELECTRICAL SIGNAL RESPONSIVE TO A PHYSICAL POSITIONING OF A SWITCHING MEMBER AND ZERO SIGNAL RESPONSIVE TO ANOTHER POSITION OF SAID MEMBER AND COMPRISING IN COMBINATION: A SOURCE OF ALTERNATING CURRENT; A SERIES IMPEDANCE FOR SAID SOURCE; A COIL HAVING A SATURABLE CORE AND A CAPACITANCE IN RESONANT CIRCUIT CONNECTION THEREWITH; MEANS CONNECTING SAID RESONANT CIRCUIT TO SAID SOURCE THROUGH SAID IMPEDANCE; A MAGNETIC SWITCH MEMBER; MEANS FOR POSITIONING SAID MAGNETIC MEMBER A PRE-DETERMINED SPACING FROM SAID CORE; MEANS CONTROLLING THE VOLTAGE OF SAID SOURCE TO A VALUE SUFFICIENT ONLY TO TRIGGER RESONANCE IN SAID CIRCUIT AT SAID PRE-DETERMINED SPACING; MEANS FOR EXTRACTING A RESONANT ELECTRICAL CURRENT SIGNAL FROM SAID CIRCUIT RESPONSIVE TO THE POSITIONING OF SAID MAGNETIC MEMBER AT SAID PRE-DETERMINED SPACING FROM SAID CORE; AT LEAST ONE OTHER RESONANT CIRCUIT IN PARALLEL CONNECTION TO SAID SOURCE AND IMPEDANCE WITH SAID FIRST MENTIONED RESONANT CIRCUIT AND HAVING A SIMILAR COIL SATURABLE CORE AND CAPACITANCE; MEANS SUPPORTING SAID CORES FOR SAID COILS IN PRE-DETERMINED SUCCESSIVE SPACING BETWEEN ADJACENT CORES; AND MEANS CONVEYING THE SAID MAGNETIC MEMBER SUCCESSIVELY INTO ASSOCIATION WITH SAID CORES AT SAID PRE-DETERMINED DISTANCE THEREBY TO EXTINGUISH A RESONANT CONDITION IN SAID FIRST MENTIONED CIRCUIT WHILE CAUSING THE GENERATION OF A RESONANT CONDITION IN THE SUCCESSIVE CORE AND CIRCUIT. 